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quiver/lib/src/iterables/merge.dart

-// Copyright 2013 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-part of quiver.iterables;
-
-/**
- * Returns the result of merging an [Iterable] of [Iterable]s, according to
- * the order specified by the [compare] function. This function assumes the
- * provided iterables are already sorted according to the provided [compare]
- * function. It will not check for this condition or sort the iterables.
- *
- * The compare function must act as a [Comparator]. If [compare] is omitted,
- * [Comparable.compare] is used.
- *
- * If any of the [iterables] contain null elements, an exception will be
- * thrown.
- */
-Iterable merge(Iterable<Iterable> iterables,
-        [Comparator compare = Comparable.compare]) =>
-    (iterables.isEmpty) ? const [] : new _Merge(iterables, compare);
-
-class _Merge extends IterableBase {
-  final Iterable<Iterable> _iterables;
-  final Comparator _compare;
-
-  _Merge(this._iterables, this._compare);
-
-  Iterator get iterator => new _MergeIterator(
-      _iterables.map((i) => i.iterator).toList(growable: false), _compare);
-
-  String toString() => this.toList().toString();
-}
-
-/// Like [Iterator] but one element ahead.
-class _IteratorPeeker {
-  final Iterator _iterator;
-  bool _hasCurrent;
-
-  _IteratorPeeker(Iterator iterator)
-      : _iterator = iterator,
-        _hasCurrent = iterator.moveNext();
-
-  moveNext() {
-    _hasCurrent = _iterator.moveNext();
-  }
-
-  get current => _iterator.current;
-}
-
-class _MergeIterator implements Iterator {
-  final List<_IteratorPeeker> _peekers;
-  final Comparator _compare;
-  var _current;
-
-  _MergeIterator(List<Iterator> iterators, this._compare)
-      : _peekers = iterators.map((i) => new _IteratorPeeker(i)).toList();
-
-  bool moveNext() {
-    // Pick the peeker that's peeking at the puniest piece
-    _IteratorPeeker minIter = null;
-    for (var p in _peekers) {
-      if (p._hasCurrent) {
-        if (minIter == null || _compare(p.current, minIter.current) < 0) {
-          minIter = p;
-        }
-      }
-    }
-
-    if (minIter == null) {
-      return false;
-    }
-    _current = minIter.current;
-    minIter.moveNext();
-    return true;
-  }
-
-  get current => _current;
-}